Fatigue and Microstructural Properties of Quenched Ti-6Al-4V. A Crystallographic Study of Fatigue Damage in Titanium. Corrosion and Corrosion-Fatigue Behavior of Ti-4.5Al-5Mo-1.5Cr (Corona 5) and Ti-6Al-4V.

Abstract : The mechanical properties and microstructures of Ti-6Al-4V were determined for specimens heat treated at temperatures from 84 C to 1065 C for 10 minutes and water quenched; these properties were compared with those of alpha'-Beta annealed specimens. Specimens heat treated at 900 C and water quenched had higher fatigue lives by a factor of four to ten relative to the other treatments, in addition this treatment resulted in high ductility, yield strength, tensile strength and elastic modulus. Microstructure studies utilizing optical and transmission microscopy showed that the improved fatigue lives were a result of strain induced transformation of retained beta to alpha' martensite. Isothermal aging of as quenched specimens reduced the fatigue lives and the retained beta was thermally activated to transform to alpha' martensite. the beta to alpha' martensite transformation observed was therefore an isothermal martensite transformation whereas it is presently assumed that this transformation is always athermal. The amount of retained beta and its relative stability was shown to depend upon the heat treatment temperature.